Kangaroo Anyone? What Is a Healthy Diet?

Most nutritionists would never recommend an Atkins diet. We cannot be sure whether a diet high in fat and low in carbohydrates is safe for our health, because we do not have scientific evidence to prove it. But, as Gary Taubes argues in the December 2012 issue of Nature, we do not have enough evidence to prove that diets that are recommended by the majority of nutritionists and health organizations are healthy either. Some leading nutritionists also questioned benefits of food believed to be a healthy staple for many decades. Recently, Harvard nutritionist Walter Willett warned adults against drinking milk, not only questioning its health benefits but also arguing that milk consumption may increase risk of developing some diseases.

Some scientists have argued that human physiology and metabolism are best suited to our past Paleolithic environment, and that means also Paleolithic diet. A very suggestive example illustrating the poor fit between human physiology and modern lifestyle is the case of our craving for “unhealthy” foods.

Many people try to reduce intake of sweet and fatty foods but often find it impossible to do. This is not surprising. These tastes have always served as the most trustworthy indicators that food has a high energy content. Energy was in limited supply in the environment of our evolutionary past, and individuals who craved and actively sought such energy-dense foods were in better nutritional shape then those who preferred the taste of energy-poor foods such as leaves or roots. Danger of overeating was not a problem because foods with a high fat and sugar content were hard to find in the Paleolithic environment. For example, the meat of wild animals has a much lower fat content than the meat of farm animals, while the only foods with a high sugar content in our evolutionary past were difficult-to-find wild honey, and ripe fruits, which were available only seasonally for short periods of time.

The scarcity of high-fat, high-sugar foods in the human evolutionary environment is unfortunate for us. Had they been more common, physiological adaptations would have most likely evolved to allow increased consumption without negative consequences for human health. Our evolutionary legacy can be blamed for the fact that today the many people who have easy access to unlimited food resources also have an evolved taste for fat and sugar, while lacking the physiology to handle it without negative health consequences.

The Paleolithic-type diet, matched to our evolved physiology and metabolism, seems like an appropriate recommendation for modern humans. Promoting a Paleolithic diet is, however, not free from problems either. First, there was no such a thing as a universal Paleolithic diet. During human evolutionary times, even though all humans lived as hunters and gatherers, incredible variation in food consumption existed both over time and between various regions.

However, while this great variability in evolutionary diets is well documented, some common patterns have been established as well. No society consumed high amounts of simple carbohydrates (i.e., sugars) and all societies consumed animal protein, often in high quantities. Putting aside Arctic populations, where fatty meats were easily accessible, meat was mostly very lean compared with the meat of domesticated animals consumed today, and thus consumption of saturated fats was low. Diets included a large variety of plants and involved a very high intake of vitamins and minerals.

Knowledge about Paleolithic diets and the evolutionary patterns of food consumption is important not only for finding the optimal diet. This knowledge also allows us to understand why people are so prone to overeating. We have some physiological mechanisms limiting the amount of food we are able to eat, but these limits are set very high. Australian Aborigines, when leading their traditional hunting and gathering way of life, were known to eat 2 to 3 kilograms of meat during one long meal. Of course, occasions when so much meat was available were rare, usually only when a kangaroo was killed; once that happened, people took maximum advantage of the situation. It has been suggested that the ability to consume a lot of food during these infrequent “feasts” was very important for the survival of hunter-gatherers. A surplus of energy, stored as body fat, provides crucial energy reserves during periods of food shortages. In Paleolithic environments, people most likely stored little food and they usually consumed everything shortly after gathering or hunting. Storing food was impractical for several reasons: It could be stolen, it had to be shared, and quite simply, preventing it from going bad was technologically difficult.

This tendency to eat all available food in one sitting was not lost with the Australian Aborigines’ transition from a traditional to a modern lifestyle. Kerin O’Dea from the University of South Australia has documented that store-bought meat, usually cheap and fatty beef or lamb, is often still consumed by westernized Aborigines in very large quantities - but with one very important difference. Three kilograms of lean meat, such as kangaroo, provided about 3,000 kilocalories. This seems like a lot, but it pales in comparison to the same amount of meat from domesticated animals, which yields up to 12,000 kilocalories!

The importance of eating regular meals, avoiding snacking, and beginning the day with a substantial breakfast are often essential aspects of modern nutritional recommendations. Such recommendations, however, have little to do with the evolutionary pattern of human consumption. People ate whenever food was available. Many hunter-gatherers had one main meal during the day, in the late afternoon after having returned to camp with food gathered or hunted that day. Snacking during the day was a typical component of the evolutionary dietary consumption. Small quantities of grubs, fruit, gum, ants, and honey from wild bees were eaten constantly.

A problem with recommending Paleolithic diets that is not much discussed is that modern humans may have different dietary needs than their ancestors, owing to differences in lifestyles, especially in terms of physical activity and reproductive patterns. It is obvious, for example, that the caloric intake appropriate for a hunter-gatherer would be much too high for a sedentary office worker. The same can be true for certain nutrients. Low levels of physical activity, and in women lower nutritional requirements resulting from a reduced reproductive output (that is: fewer babies), may mean that the nutritional requirements for vitamins and minerals are lower for modern people than they were for our ancestors.

Despite all the methodological challenges of research in this area, a conclusion might be drawn that Paleolithic diets are much more appropriate for modern humans than other diets, especially diets that are agriculture-based. If so, why is their importance not supported by epidemiological studies? The Mediterranean diet (and especially the traditional diet of rural populations from this region), and the Japanese diet, both of which are agriculture-based diets, are frequently shown to be associated with a lower risk of metabolic diseases, and such findings influence public health recommendations. But the health benefits of Paleolithic diets are almost never discussed by epidemiologists. One reason for this state of affairs immediately comes to mind, namely that epidemiological findings are mostly based on studies with sample sizes large enough for different causes of morbidity and mortality to be analyzed. Unfortunately, Paleolithic diets are not a popular topic of research, and thus they are not even considered by the organizations that provide recommendations about healthy lifestyles.

The jury is still out on which diet is the best for us, but a personalized approach is a recommended option. Try to eat something close to the diet of our evolutionary ancestors—lots of vegetables (in fact, as much as you can eat), lean meat, fish, eggs. Limit sugar (and that includes fruit!) and do not eat too much grains, rice and pasta. Importantly, monitor your health. If you notice undesired changes in your blood pressure, cholesterol levels or body weight, make changes and adjust how you’re eating. And unfortunately, because it is against out innate preference for inactivity, exercise is a must. Wonder diets may sometimes work, but what most of us need is not a crash diet, but a sensible way of eating that can be followed for a lifetime.